This invention pertains to compositions containing a particular class of liquid crystalline polyesters and one or more aromatic phosphonites. This invention also pertains to a process for preparing liquid crystalline polyesters in the presence of one or more aromatic phosphonites.
Liquid crystalline polyesters (LCPs) are unique among polymers because they have very high tensile, flexural, and temperature resistance properties which are very desirable properties for high performance applications, such as in structural applications and in electronic applications. U.S. Pat. No. 4,169,933 discloses a group of liquid crystalline polyesters which consist essentially of residues of terephthalic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone, and p-hydroxybenzoic acid. It is highly desirable that these types of LCPs have the very best thermal stability so that their molecular weight is maintained, i.e., during their preparation and injection molding, extrusion, etc., into the many end uses that have been identified where they show superior performance. Unless measures are taken during the preparation of such liquid crystalline polyesters, the polymerization rate may be so rapid that an appreciable amount of the starting materials may be lost due to co-distillation, sublimation, or other means. Loss of starting materials may lead to (a) loss of stoichiometry, (b) reduced yield of polymer, and (c) plugging or partial plugging of the reactor condensing system due to the solids being co-distilled or sublimed. Also, when the polymerization rate is very fast, it is more difficult to control the process and produce a predetermined molecular weight or inherent viscosity (I.V.).
It is an object of this invention to provide novel compositions containing one or more liquid crystalline polyesters. It is also an object of this invention to provide liquid crystalline polyesters comprising certain levels of terephthalic acid, cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone, biphenol and/or p-hydroxybenzoic acid where the rate of polymerization of LCPs is slowed when prepared to high molecular weight/IV in the melt so that stoichiometry is better maintained, high yields of polymer are maintained, plugging of the reactor condensing system is minimized or eliminated, and the preparation of LCPs having predetermined molecular weights/IV""s is facilitated.
It is also an object of this invention to provide a process for preparing compositions containing certain LCPs in the presence of certain levels of one or more aromatic phosphonites. The new process of the invention enables the preparation of LCPs in a more controllable manner and produces products having improved thermalloxidative stability.
This invention relates to a composition comprising:
A. a liquid crystalline polyester derived from:
(I) diacid residues selected from terephthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, biphenyl dicarboxylic acid and naphthalenedicarboxylic acid;
(II) diol residues selected from hydroquinone, resorcinol, and biphenol, and
(III) optionally, diacid residues selected from p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 6-hydroxy-2-naphthoic acid,
wherein the moles of the diol residues are equal to the moles of the diacid residues and the total of the I and II or the I, II and III mole percentages are based on the total residues which make up the liquid crystalline polyester; and
B. one or more aromatic phosphonites.
This invention further relates to the process of preparing certain liquid crystalline polyesters in the presence of one or more aromatic phosphonites wherein said one or more phosphonites are added to the monomer charge and/or to derived prepolymers prior to polycondensation.
The invention relates to compositions comprising certain liquid crystalline polyesters and one or more aromatic phosphonites as well as a process for preparing the compositions. More specifically, the invention relates to a composition comprising:
A. a liquid crystalline polyester derived from:
(I) diacid residues selected from terephthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, biphenyl dicarboxylic acid and naphthalenedicarboxylic acid;
(II) diol residues selected from hydroquinone, resorcinol, and biphenol, and
(III) optionally, diacid residues selected from p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 6-hydroxy-2-naphthoic acid;
wherein the moles of the diol residues are equal to the moles of the diacid residues and the total of the I and II or the I, II and III mole percentages are based on the total residues which make up the liquid crystalline polyester; and
B. one or more aromatic phosphonites.
Preferred examples of monomers from which component (I) may be derived are terephthalic acid; naphthalenedicarboxylic acid, preferably, 2,6-naphthalenedicarboxylic acid; and cyclohexanedicarboxylic acid, preferably, 1,4-cyclohexanedicarboxylic acid. More preferred dicarboxylic acids are terephthalic acid and naphthalenedicarboxylic acid.
Preferred examples of monomers from which component (II) may derived are hydroquinone, and biphenol, preferably 4,4xe2x80x2-biphenol.
A preferred example of a monomer from which component (III) may derived is p-hydroxybenzoic acid.
It is preferred that the LCP compositions of the invention comprise about 1.5 to about 25, preferably, about 5 to about 15 mole percent terephthalic acid (T) residues; about 6.5 to about 37, preferably, about 15 to about 25 mole percent 2,6-naphthalenedicarboxylic acid (N) residues; about 16 to 42, preferably, about 20 to about 30 mole percent hydroquinone (HQ) residues; about 17 to 67, preferably, about 30 to about 50 mole percent p-hydroxybenzoic acid (PHB) residues; where the total mole percent of T, N, HQ and PHB is equal to 100.
Particularly, the LCP compositions of the invention comprise about 0.01 to 5.0 weight % of one or more aromatic phosphonites, preferably 0.5 to 3.0 weight %, more preferably, 0.1 to 2.0 weight % based on the total polymer weight.
The LCP compositions of the invention preferably have the following characteristics: the T:N molar ratio is about 10:90 to about 60:40, preferably about 20:80 to about 40:60, where the moles of HQ are equal to the total moles of T and N, the liquid crystalline polyesters have melting points determined by differential scanning calorimetry (DSC) equal to or less than 375xc2x0 C.
The aromatic phosphonites of the present invention generally have the following structure: 
wherein A2 is independently selected from the group consisting of oxygen or a chemical bond; R6 is an aromatic radical and R7 is independently selected from the group consisting of aliphatic or aromatic radicals. It is preferred that A2 is a chemical bond. It is also preferred that R6 is 4,4-biphenylene. It is further preferred that R7 is substituted aryl. It is even further preferred that A2 is a chemical bond, R6 is 4,4biphenylene, and R7 is substituted aryl.
Preferably, the aromatic phosphonites useful in the invention have the following structure: 
wherein A2 is independently selected from the group consisting of oxygen or a chemical bond; A3 is a chemical bond, S, SO2, O, CO, alkylene or alkylidene containing from 1 to about 8 carbon atoms; and R7 is independently selected from the group consisting of aliphatic radicals containing from about 1 to 25 carbon atoms, or substituted or unsubstituted aromatic radicals of from about 6 to30 carbon atoms. The R7 groups in all of the structures are preferably independently selected from the group consisting of the following: methyl; ethyl; isopropyl; butyl; isobutyl; t-butyl; phenyl; linear or branched alkyl from about 1 to about 25 carbon atoms; aryl substituted phenyl containing about 6 to 30 carbon atoms; halogen substituted phenyl; hydroxy substituted C6 to C30 aryl; naphthyl; C1 to C25 alkyl or C6 to C30 aryl; substituted naphthyl; and halogen substituted naphthyl.
It is preferred that R7 is selected from the group consisting of the following: phenyl; aryl substituted phenyl containing about 6 to 30 carbon atoms; halogen substituted phenyl; naphthyl; C6 to C30 aryl; substituted naphthyl; and halogen substituted naphthyl.
It is more preferred that R7 is selected from C1-C8 substituted aromatic radicals. R7 is, even more preferrably, one or more t-butylphenyl pendent groups.
The preferred R7 groups of the invention are independently selected from the structures: 
wherein R8 is independently selected from an alkyl group of about 1 to 6 carbon atoms. It is preferred that R8 is t-butyl.
Even more specifically, the R7 groups as represented in all of the structures depicted herein are preferably independently selected from the structures: 
In particular, two of the more preferred phosphonites of the invention includes tetrakis [2,4-di-tert-butyl-phenyl]-4,4xe2x80x2-biphenylene diphosphonite and tetrakis [2,6-di-tert-butyl-phenyl]-4,4-biphenylene diphosphonite.
Even more particularly, the more preferred phosphonites of the invention have one of the following structures: 
The LCP polyesters of the invention may be prepared by any method known in the art, i.e., U.S. Pat. No. 4,169,933.
The LCP polyesters in the invention may have inherent viscosities of about 3 to about 11 dL/g, preferably about 5 to about 10 dL/g, measured at 25xc2x0 C. in 60:40 by weight pentafluorophenol/1,2,4-trichlorobenzene at 0.1 g/100 mL in a Schoft Gerate viscometer.
However, this invention also involves the process of preparing liquid crystalline polyesters (LCPs) as described above in the presence of one or more aromatic phosphonites. All of the embodiments of the compositions described herein apply to the process embodiments described herein. Any composition described herein is capable of being prepared by the process of the invention. Preferred compositions of the invention are also preferred in the process of the invention.
The process of the invention may be practiced by those skilled in the art, such as by heating a mixture of the dicarboxylic acids, the acyl derivatives of aromatic dihydroxy compounds and p-hydroxybenzoic acid, and the aromatic phosphonite compound with or without a catalyst to form the LCP and a volatile carboxylic acid. The aromatic phosphonite compound(s) are, preferably, added with the initial charge of monomers. Alternatively, the process of the invention may be practiced by heating a mixture of the dicarboxylic acid(s), aromatic dihydroxy compound(s), hydroxycarboxylic acid (if used), and aromatic phosphonite compound(s) in a reactor with an aliphatic acid anhydride (such as acetic or propionic anhydride) in the presence or absence of a catalyst, to first carry out the acylation of the hydroxy groups and then effect the polycondensation reaction by further heating at a temperature sufficiently high to maintain the polymer in the molten state while applying vacuum to increase the inherent viscosity (IV)/molecular weight to the desired level.
It is preferred that the aromatic phosphonite compound(s) be added prior to polycondensation. The phosphonite compound may be added with the initial monomer charge. It also may be added during polymerization after the LCP polymer attains an inherent viscosity of about 0.3 to 3.0 dL/g (the pre-polymer stage). For those skilled in the art, a useful variation of this alternative method is the separate acylation of the hydroxy-containing monomers in a first reactor, transferring this product to a second reactor, adding the dicarboxylic acid(s), and carrying out the polycondensation reaction as before described. The aromatic phosphonite compound(s) may be added to the first or second reactor in this multi-step process.
Also, the process of the invention may include the preparation of a relatively low molecular weight prepolymer by one of the previously described methods and further polymerizing it to high molecular weight by solid-state polymerization techniques well known to those skilled in the art.
This use of the aromatic phosphonite(s) in this solid-state polymerization method is also a very desirable variation of the process of the invention. Also, the process of the invention may include heating the previously described materials with or without a catalyst in an extruder to form a prepolymer which may be further polymerized to high molecular weight by solid-state polymerization techniques well known to those skilled in the art. The composition of the invention may also be prepared by melt polymerization.
Suitable catalysts include dialkyl metal oxide (preferably dialkyl tin oxide), diaryl metal oxide (preferably diaryl tin oxide), titanium dioxide, alkoxy titanium silicates, titanium alkoxides, alkali metal and alkaline earth metal salts of carboxylic acids (preferably sodium acetate), gaseous acid catalysts such as Lewis acids (e. g., BF 3), hydrogen halides (e. g., HCI), and the like. The quantity of catalyst utilized is typically about 50 to about 500 parts per million, based on the total weight of starting materials (less the acyl anhydride, if any, used as described below). If a multi-step reaction process is used as above described, the catalyst may be added to the acylation or polycondensation steps. For purposes of this invention, the use of about 50 to about 200 parts per million by weight of at least one alkali metal-containing catalyst is sufficient.
The process of the invention has the advantage of a slower and more controllable reaction rate when the LCP is built up to high molecular weight by a melt phase procedure. Advantages of the reduced polymerization rate include (a) a more easily controllable process and (b) fewer process problems such as plugging of the reactor condensing system with monomers (such as hydroquinone, hydroquinone diacetate, or terephthalic acid) that have significant volatility to co-distill and/or sublime during the process.
The LCP compositions prepared by the process of the invention are useful for a variety of end uses requiring a combination of good tensile and flexural properties coupled with the excellent moldability (shear-thinning behavior) and thermal stability required when extruding or injection molding intricately designed parts.
The LCP compositions prepared by the process of the invention are also useful in extruded or blown film applications requiring exceptional barrier properties or chemical resistance and as an overlay for corrosive applications. When filled with glass fibers or other fillers, they are useful for electronic applications, electrical connectors, and structural applications.
The LCP compositions prepared by the process of the invention may contain various additives and fillers. These additives may be compounded with the LCP compositions by methods well known to those skilled in the art, such as by extrusion of a physical mixture of the materials in an extruder. Some of these materials (such as carbon black) may be added to the reactor before or during the preparation of the LCPs.
The fillers may be in fibrous, particulate, or flaky form, depending on the intended use of the material. Preferred additives include antioxidants, titanium dioxide, carbon black, clay, flame retardants, drip suppressants and other pigments.
Examples of fibrous fillers include inorganic fibrous materials such as glass fiber, silica fiber, silica/alumina fiber, alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, boron fiber, potassium titanate fiber, and fibrous materials of metals such as stainless steel, aluminum, titanium, copper, and brass. Glass fiber is especially useful as a fibrous filler. It is also possible to use high-melting organic fibrous materials such as polyamide, polyester, or acrylic resin.
Examples of particulate fillers include carbon black, graphite, silica, quartz powder, glass beads, milled glass fiber, glass balloons, glass powder, silicates such as calcium silicate, aluminum silicate, kaolin, talc, clay (such Montmorillonite clay), diatomaceous earth, and wollastonite, metallic oxides such as iron oxide, titanium oxide, zinc oxide, antimony trioxide, and alumina, metal carbonates such as calcium carbonate and magnesium carbonate, metal sulfates such as calcium sulfate and barium sulfate, and various other powdery materials such as ferrite, silicon carbide, silicon nitride, and boron nitride.
Examples of flaky inorganic materials include mica, glass flake, and various metallic foils.
Examples of organic fillers include heat-resistant, high strength synthetic fibers such as an organic polyester fiber, liquid crystal polymer fiber, aromatic polyamide fiber, and polyimide fiber.
The organic and inorganic fillers may be used alone or in combination of two or more at levels up to 60 weight percent or more, and these additives may be compounded with the LCP compositions of the invention by methods well known to those skilled in the art, such a by extrusion of a physical mixture of the materials in an extruder. Also, certain of the additives, such as antioxidants or carbon black, may advantageously be added to the LCPs during polymerization.
Another preferred embodiment of the invention is a molding composition comprising a blend of any of the liquid crystalline polyester compositions described herein; and 0 to 50 weight percent and preferably at least 20 weight percent glass fibers based on the total weight of the molding composition.
It is preferred that the molding composition contain glass fibers in the amount of about 30 weight percent based on the total weight of the molding composition.
It is also preferred that the glass fiber has a thickness of about 9 to 15 microns and a length of about 0.8 to 26 mm. It is further preferred that the molded article has a thickness of less than about 1.5 mm.
The compositions of the invention are also useful as molding compositions. Also, the compositions of the invention are useful in the preparation of molded articles.